As the gross structure and anatomy of Plexaura homomalla conform closely with those of other holaxonian gorgonaceans,. P. homomalla forms arborescent colonies of substantial size (as much as 1.5 m in height) composed of a supporting axis of scleroprotein over which is spread a layer of mesogloea containing spicules (“coenenchyme” ). The polyps, or zooids, are embedded in this coenenchyme and are connected with one another by way of small canals (“solenia”) lined with entoderm, which in turn open into a series of large, longitudinal stem canals which closely surround the axis in the smallest branchlets as well as in the large branches and main stem. The surface of both coenenchyme and zooids is covered with ectoderm, and the axis is invested throughout with an ectodermal axis epithelium which is responsible for its formation. The lining of the polyps and canal system consists of entoderm, except for the two asulcal septal filaments, which are ectodermal. Pexaura homomalla has gastrodermal solenia of two distinctly different kinds and is unusual among gorgonaceans in the great extent of their development, with consequent reduction of mesogloea. A peculiarity of P. homomalla soon noticed by anyone working with it in the field or laboratory is its tendency to begin disintegrating much sooner after collection than do other species. Scanty mesogloea, which is reduced to a thin layer immediately surrounding the spicules, and thin mesolamellar sheets between the solenia and cell-strands. The spicules are not held in place by mesogloea, as they are in most other species, but by cellular tissue of a rather diffuse nature.